Rr221002-transducers-in-instrumentation

Set No. 1

Code No: RR221002

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 TRANSDUCERS IN INSTRUMENTATION ( Common to Electronics & Instrumentation Engineering and Electronics & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Describe mathematical model of measurement system. (b) A 0-150V voltmeter has a guaranteed accuracy of 1% of full scale reading. The voltage measured by this instrument is 75V. Calculate the limiting error in percent. Comment upon the result. [8+8] 2. (a) Derive the expression for time response of a 2nd order under damped system when subjected to unit step input. Sketch its response. (b) A thermometers is initially at a temperature of 70o C and is suddenly placed in liquid which is maintained at 300o+ C. The thermometer indicates 200o C after a time interval of 3 sec. calculate the time constant for the thermometer. Also calculate the temperature after 5 sec. [8+8] 3. (a) Explain in detail the constructional features and the theory of operation of the wire type strain gauge. (b) In an equal arm wheatstone bridge, the single active gauge has nominal resistance of 120 ohms, and is made of advance having a thermal coefficient of expansion of 30x10−6 m/m0 C and temperature coefficient of resistance of 12x10−6 ohm/ohm0 C. The other three arms are fixed resistors having negligible temperature coefficients. If the gauge is bounded to steel having a thermal coefficient of expansion of 13x10−6 m/m0 C. Calculate the bridge output for a 60 c rise in specimen temperature, if the gauge current is 0.25 mA. [8+8] 4. (a) Explain the phenomenon of magnetostriction and how it is used for the measurement of force. (b) Describe the constructional features of a magnetostrictive transducer and obtain the input -output relation ship. [8+8] 5. (a) Describe the different modes of operation of Piezo electric transducers. (b) Define and sketch binders and twisters. (c) Explain the application of Piezo electric transducers.

[6+6+4]

6. (a) Starting from fundamentals, derive the expression for linearized sensitivity of Electrostatic Force-balance transducer. (b) List out the performance characteristics of typical electrostatic Force-balance transducers. [8+8]

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Set No. 1

Code No: RR221002

7. (a) Draw the sketches of various forms of bimetallic thermometer. (b) Discuss various types of transducers available for measuring temperature. (c) What are the errors to be accounted in the evaluating performance of resistance thermometers? [6+6+4] 8. (a) List the detectors used in radiation and optical pyrometers. (b) Explain the factors affecting the static accuracy of filled in thermometers. [8+8] ⋆⋆⋆⋆⋆

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Set No. 2

Code No: RR221002

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 TRANSDUCERS IN INSTRUMENTATION ( Common to Electronics & Instrumentation Engineering and Electronics & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Define the following static characteristics with necessary examples and graphs: i. ii. iii. iv. v.

Accuracy sensitivity static error Dead space Drift.

(b) A voltage has a true value of 1.50 volts. An Analog indicating instrument with a scale range of 0-2.50 volts shows a voltage of 1.46 volts. What are the values of absolute error and correction? Express the error as a traction of the true value and the full-scale deflection. [10+6] 2. (a) A 2nd order instrument has a natural frequency of 4 Hz and a damping ratio of 0.66. If the excitation frequency of the system is 6 Hz, determine the error due to the proximity of excitation frequency with the natural frequency of the system. (b) Derive the expression for time response of a 2nd order system subjected to unit impulse input. Sketch its response. [8+8] 3. (a) Compare and contrast a thermocouple with a thermistor as a temperature transducer. (b) Why is platinum normally used in the construction of precision standard thermometers for calibration work? State its measuring temperature range and the reason for selecting such a range. Describe with a neat diagram and construction detail of a platinum resistance thermometer. [6+10] 4. (a) In a variable capacitance transducer the diaphragms are 20mm in diameter and 4mm apart. If a pressure produces and average deflection of 0.25mm, calculate the value of capacitance after the application of force. The capacitance before application of force is 400pf. (b) Discuss the scheme of a variable permittivity of thickness dielectric type sensor. [8+8] 5. (a) Describe the properties of materials used for Piezo-electric transducers. (b) Derive the expressions for voltage and charge sensitivities.

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[8+8]

Set No. 2

Code No: RR221002

6. (a) With a neat sketch, explain the operation of Electrostatic force-balance transducer system for the measurement of low-level (i.e. low-g), acceleration. (b) Draw the schematic block diagram and explain about Electrostatic forcebalance transducer system for low differential gas pressures. [8+8] 7. (a) What is a RTD? Where it is used? (b) Explain a 4 lead measurement scheme of temperature measurement using resistance thermometer. [6+10] 8. Describe the working and construction of resistance thermometers. Describe the materials used for RTDs along with their properties. Sketch this typical characteristic curve. [16] ⋆⋆⋆⋆⋆

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Set No. 3

Code No: RR221002

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 TRANSDUCERS IN INSTRUMENTATION ( Common to Electronics & Instrumentation Engineering and Electronics & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Explain with a block diagram an instrumentation system and explain the function of various blocks. (b) The dead-zone of a certain plyrometer is 0.125 percent of the span. The calibration is 800o C to 1800o C what temperature change must occur before it is detected? [8+8] 2. (a) Derive the expression for time response of a 2nd order under damped system when subjected to unit step input. Sketch its response. (b) A thermometers is initially at a temperature of 70o C and is suddenly placed in liquid which is maintained at 300o+ C. The thermometer indicates 200o C after a time interval of 3 sec. calculate the time constant for the thermometer. Also calculate the temperature after 5 sec. [8+8] 3. (a) What is the purpose of connecting thermocouples in parallel? (b) Suggest an instrumentation circuit for thermocouples, which will produce a linear output with temperature. (c) State two advantages of using a thermocouple for measurement of temperature. [6+4+6] 4. (a) Explain how by using a differential arrangement a capacitive transducer which works on the principle of variation of capacitance with displacement between two plates, the response can be made linear. (b) Describe the frequency response of capacitive transducers.

[8+8]

5. (a) Describe the properties of materials used for Piezo-electric transducers. (b) Derive the expressions for voltage and charge sensitivities.

[8+8]

6. (a) With a schematic diagram, explain the working of Electrodynamic Forcebalance transducer for the measurement of linear acceleration. (b) Explain the static performance of an Electrodynamic Force-balance acceleration transducer with respect to sensitivity and linearity. [8+8] 7. (a) Write short notes on Infrared LEDs. (b) Draw and explain the characteristics curve of phototransistor and photodiode. [6+10]

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Set No. 3

Code No: RR221002

8. (a) List the detectors used in radiation and optical pyrometers. (b) Explain the factors affecting the static accuracy of filled in thermometers. [8+8] ⋆⋆⋆⋆⋆

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Set No. 4

Code No: RR221002

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 TRANSDUCERS IN INSTRUMENTATION ( Common to Electronics & Instrumentation Engineering and Electronics & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Define the following static characteristics with necessary examples and graphs: i. ii. iii. iv. v.

Accuracy sensitivity static error Dead space Drift.

(b) A voltage has a true value of 1.50 volts. An Analog indicating instrument with a scale range of 0-2.50 volts shows a voltage of 1.46 volts. What are the values of absolute error and correction? Express the error as a traction of the true value and the full-scale deflection. [10+6] 2. (a) A 2nd order instrument has a natural frequency of 4 Hz and a damping ratio of 0.66. If the excitation frequency of the system is 6 Hz, determine the error due to the proximity of excitation frequency with the natural frequency of the system. (b) Derive the expression for time response of a 2nd order system subjected to unit impulse input. Sketch its response. [8+8] 3. (a) Derive an expression for gauge factor of a strain gauge. Also find an expression for a four arm active Wheatstone bridge output used to measure strain. (b) Explain the classification of strain gauges with their salient features.

[8+8]

4. (a) Show how output voltage signals proportional to linear displacements imparted to the movable plate of a parallel plate capacitor. (b) Discuss the problems encountered while measuring small displacements by capacitive transducers. [8+8] 5. (a) Describe the properties of materials used for Piezo-electric transducers. (b) Derive the expressions for voltage and charge sensitivities.

[8+8]

6. (a) With a schematic diagram, explain the working of Electrodynamic Forcebalance transducer for the measurement of linear acceleration. (b) Explain the static performance of an Electrodynamic Force-balance acceleration transducer with respect to sensitivity and linearity. [8+8] 7. (a) Explain briefly the methods used to measure the output from thermocouples. 1 of 2

Set No. 4

Code No: RR221002

(b) A chromel-alumel thermocouple having a linear relationship between temperature and emf indicates zero at 00 C and 45.14 mV at 11000 C. The thermocouple is exposed to a temperature of 8400 C with cold junction maintained at 250 C, calculate the induced emf. [8+8] 8. (a) List the detectors used in radiation and optical pyrometers. (b) Explain the factors affecting the static accuracy of filled in thermometers. [8+8] ⋆⋆⋆⋆⋆

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